The Scottish physician John Ferriar (1761-1815) was a well-known natural philosopher as well as a critical thinker of wide repute. His 1813 Essay Towards a Theory of Apparitions made the case that ghosts were optical illusions. A much earlier paper, "Of Popular Illusions, and Particularly of Medical Demonology," contains much material of interest to the skeptic. In this excerpt, Ferriar discusses the origins of the vampire myth (a topic of great interest in the eighteenth century due to an alleged vampire outbreak in Hungary) by examining a firsthand account of a vampire attack. He applies skeptical reasoning to conclude that a combination of ignorance, fear, and unscrupulous religious practitioners was at fault--a conclusion that is almost undoubtedly right.

From "Popular Illusions"Read before the Manchester Literary and Philosophical Society, May 12, 1786

Some questions, apparently puzzling, occur on the subject of [vampire] disturbances: how could all the inhabitants of considerable towns be imposed on, in a matter so nearly respecting the peace and safety of each individual, as universally to impute actions to supernatural influence, which perhaps were no more than knavish? How could they be deceived in the solemn and public inspection of the Vampire's body, which always took place? And how could the destruction of a wretched carcase, long dead, become the means of restoring public tranquillity, so as to be ordered by the magistrates? The best explanation is, to shew, by unquestionable facts, how such delusions have taken place; this will also elucidate the nature of all the illusions already mentioned. When [French botanist Joseph Pitton de] Tournefort visited the island of Mycone, in 1701, the principal town, at which he resided, was disturbed by a vroucolacas, or redivivus; the consternation was so great, that most of the inhabitants slept in tents, in the market-place: their peace was restored by burning the carcase of the redivivus, after a public examination, in which it was declared to be fresh. These are the principal facts, and apparently strong: now let us unveil their origin, by an abstract of Tournefort's observations.

I. Tournefort observes, that the person accused of those disturbances had been quarrelsome during his life, and was murdered privately. So that he was a proper subject of suspicion; supposing the general delusion once established.

II. The redivivus was accused of nothing which might not have been practised by ordinary vagabonds; "he was seen to walk in the night "with great haste; he tumbled about people's "goods, put out their lamps, &c." The wonders related of the German redivivi are only exaggerations.

III. The story never gained full credit, till the papas, (priests) for their own honour and interest, took it up.

IV. During the examination at the chapel, the popular fury against the deceased carried every thing before it:

"the corpse stunk so offensively, that they were obliged to burn frankincense; but the smoke mixing with the exhalations from the carcase, increased the stench, and began to affect the poor people's brains. Their imaginations, struck with the spectacle before them, became full of visions. They fancied that a thick smoke arose out of the body; we durst not say it was the smoke of the incense. They were incessantly bawling out vroucolacas **** Several people present averred that the wretch's blood was extremely red: the butcher swore the body was still warm **** Just at that instant came in a flock of people, loudly protesting they plainly perceived that the body was not grown stiff, when it was carried from the fields to church, to be buried, and that consequently it was a true vroucolacas **** I do not doubt but they would have sworn it did not stink, if we had not been there **** And for us, who had got as close to the corpse as we could, that we might be more exact; in our observations, we were almost poisoned by the intolerable stench that issued from it. When they asked us what we thought of this body," (every one knows that Tournefort was a physician) "we told them we believed it to be "thoroughly dead; but as we were willing to cure, or at least not to exasperate their prejudiced imaginations, we represented to them, that it was no wonder the butcher should feel "a little warmth, when he groped among the putrid intestines; that it was no extraordinary thing for the body to emit fumes, since dung turned up will do the same; that as for the pretended redness of the blood, it still appeared, by the butcher's hands, to be nothing but a very foetid, nasty smear."

V. The devil took care to get into the cellars of those persons who abandoned their houses, in order to drink up their wine.

VI. No watch was kept, nor any proper measures taken to prevent villanous practices.

Upon the whole then, the opinion of a vroucolacas, like the others already examined, appears to be only an hypothesis, formed to account for phænomena, whose causes were not obvious to the people. But if a philosopher had not unluckily been present at this curious transaction, the annals of credulity could scarce have furnished a stronger proof than this, of the existence of redivivi, consequently of all sorts of demoniacal operations.

It seems also, that when men are unacquainted with the natural cause of a particular appearance, and at the same time, are persuaded of the possibility of diabolical illusions, they will impose even on their own senses, to favour the admission of a theory so interesting to their imaginations.

Source: John Ferriar, “Of Popular Illusions, and Particularly of Medical Demonology,” Memoirs of the Literary and Philosophical Society of Manchester 3 (1790): 87-91.